1. Field of the Invention
This invention relates generally to a method and apparatus for controlling internal combustion engines and more particularly to a feedback-compensated ramp-type analog-to-digital converter usable in such a control system.
2. Statement of the Prior Art
Many of the patents of the prior art recognize the need for employing the enhanced accuracy of digital control systems for more accurately controlling one or more functions of an internal combustion engine.
U.S. Pat. No. 3,969,614 which issued to David F. Moyer, et al on July 13, 1976 is typical of such systems as are U.S. Pat. No. 3,835,819 which issued to Robert L. Anderson, Jr. on Sept. 17, 1974; U.S. Pat. No. 3,904,856 which issued to Louis Monptit on Sept. 9, 1975; and U.S. Pat. No. 3,906,207 which issued to Jean-Pierre Rivere, et al on Sept. 16, 1975. All of these Patents represent a break-away from the purely analog control systems of the past, but neither the accuracy, reliability, or number of functions controlled is sufficient to meet present day requirements.
Future internal combustion engines will require that emissions be tightly controlled due to ever-increasing governmental regulations, while fuel consumption is minimized and drivability improved over the entire operating range of the engine. None of the systems of the prior art provide a method and apparatus for controlling the operation of an internal combustion engine over its entire operating range while maintaining sufficient accuracy to achieve minimal emissions and minimal fuel consumption together with improved drivability.
The analog-to-digital converter systems used in the prior art are relatively inaccurate thereby preventing the engine control systems in which they were used from being reliable. Furthermore, the analog-to-digital control systems of the prior art in general do not teach A/D conversion systems capable of maintaining the degree of accuracy obtainable by applicant's feedback-compensated system.